Amancio Ortega Gaona, already the world’s fourth-richest person based on the success of his Zara fashion retail stores, has quietly amassed a real estate empire worth as much as $10 billion and is emerging as a formidable competitor for prime properties from London to Beverly Hills. Relying on all-cash offers, he has outbid the world’s biggest institutional funds and professional property investors. ...

The precise value of his empire is unclear. He has spent at least $6 billion over the past decade in cities including Berlin, Paris, Chicago, Boston, Miami, Washington and San Francisco, according to Real Capital Analytics and public records. ...

At least two of Ortega’s London properties are owned through Luxembourg entities, which he inherited from the previous owners, records show. Using subsidiaries in Luxembourg, which has lenient capital gains tax rules, is a common tactic among investors. Inditex also uses tax-haven subsidiaries. As reported by Bloomberg News in February, the retailer has shifted $2 billion of profits into a low-tax unit in the Netherlands and Switzerland, helping cut its income tax bill around the world.